1. Field of the Invention
The invention relates to a driving amplifier, and more particularly, to a driving amplifier that utilizes a digital control for automatically controlling sourcing and sinking of current.
2. Description of the Prior Art
In amplifier design there is always a trade-off between efficiency and crossover distortion. A conventional AB current driving amplifier comprises an operational amplifier coupled to a push-pull stage, to push or pull (source or sink) a current from the load. When sourcing current to the load, a PMOS driver will be utilized, and when sinking current from the load, an NMOS driver will be utilized. Conventional AB class amplifiers utilize a small amount of biasing current to ensure a smoother crossover. If the bias current is too small the amplifier will still suffer some crossover distortion. Furthermore, if both drivers are carrying large currents then a shoot-through current from the power supply may be generated. Therefore, accurate control of the bias current is essential.
A class AB amplifier that has three stages for reducing these problems is disclosed in “A CMOS Large-Swing Low-Distortion Three-Stage Class AB PowerAmplifier”, published in the IEEE journal of solid-state circuits, Vol. 25, No. 1, February 1990, and is included herein by reference. This circuit improves on other conventional implementations, but has complicated circuitry. It is therefore desirable to provide a new operational amplifier that simplifies the circuitry of the above-described three-stage amplifier, while reducing the amount of current carried by the drivers.